1. Field of the Invention
The present invention relates to an apparatus and a method for regulating pressures in two chambers, for example, a multi-chamber semiconductor process apparatus.
2. Information of the Related Art
In general, in manufacturing semiconductor integrated circuits, semiconductor wafers are subjected to various processes, such as film deposition, etching, etc. Conventionally, this series of processes is executed in a manner such that the semiconductor wafers are takes out in a batch from one process apparatus after undergoing a specific process therein, and are transported in the atmosphere to another process apparatus for the next process. According to this method, the efficiency of operation is not very high, due to the inevitable transportation in the atmosphere after the completion of every process.
Recently, therefore, a so-called multi-chamber process apparatus has been developed in order to improve the operating efficiency of the processes. In this apparatus, a plurality of different sheeter-type process units for the aforesaid series of processes are combined together so that the semiconductor wafers having undergone one process can be delivered to another process without being exposed to the atmosphere.
In the multi-chamber semiconductor process apparatus of this type, for example, a film deposition chamber and a etching chamber are connected to a transfer chamber which is always kept in a vacuum. The transfer chamber is coupled with a small-capacity load locking chamber whose internal pressure is changed as required between the levels of a vacuum pressure and the atmospheric pressure. Thus, the wafers can be delivered between the transfer chamber and the load locking chamber without breaking the vacuum in the transfer chamber.
In order to prevent natural oxidation of the wafer surface, moreover, the load locking chamber is loaded with an inert gas, e.g., nitrogen gas, and is coupled with a loader chamber which is always kept substantially at the atmospheric pressure. Thus, the wafers introduced into the apparatus can be delivered between the load locking chamber and the loader chamber.
In a manufacturing process for semiconductor wafers, workpieces are subjected to micron-order machining, so that the existence of a very small quantity of dust or particles may easily result in defective products. How to remove these particles is an essential problem.
In these circumstances, a gas or air inevitably flows into one of the two connected chambers due to the difference in pressure between the chambers as the semiconductor wafers are delivered between them. In some cases, therefore, particles are flung up and caused to adhere to the wafers. In internally connecting the load locking chamber, whose internal pressure is repeatedly changed between the levels of the vacuum and atmospheric pressures, and the loader chamber which is always kept substantially at the atmospheric pressure, in particular, the two chambers are tentatively subjected to a pressure difference in advance so that they can be caused to communicate with each other by opening a gate valve between them when the internal pressure of the load locking chamber is raised substantially to the level of the atmospheric pressure by the nitrogen gas supply.
As yet, however, there is no high-accuracy pressure sensor which can cover a pressure range as high as the atmospheric pressure and can accurately measure pressure differences of a level such that no gas flows. Even when a zero differential pressure is detected by the pressure sensor, therefore, the gas may possibly flow and fling up particles with every connection of the chambers due to a pressure difference which is involved in an error in measurement.
In the modern technology which handles semiconductor devices of higher density and finer configuration, in particular, the presence of the scantiest particles may cause a reduction in yield. Thus, there is a demand for an immediate solution to this problem.